The problem was suggested by Professor G. I. Taylor as being of interest and importance in the phenomena of rupture in a solid, due to the presence of a crack, and the slip in a crystal. In experiments on the distortion of a crystal of aluminium under a tensile stress the conclusion is reached that “…as far as these experiments go, the distortion of a crystal of aluminium under compression is of the same nature as the distortion which occurs when a uniform single-crystal bar is stretched. The distortion is due to slipping parallel to a certain crystal plane and in a certain crystallographic direction, and the choice of which of twelve possible crystallographically similar types of slipping actually occurs depends only on the components of shear stress in the material and not at all on whether the stress normal to the slip plane is a pressure or a tension.”